Hydraulic lift with weight transfer

ABSTRACT

Lift structure particularly useful with front mounted implements for providing both lift and weight transfer functions from a single valve. The valve acts as an adjustable bleeder for the lift cylinder and includes a control knob which is movable both axially and rotationally to respectively provide lift and adjustable flotation. The valve is normally biased to an adjustable orifice position for operating the implement in a lowered, flotation position. To momentarily lift the implement, the operator moves the control knob against the bias to direct flow to the lift cylinder thereby raising the implement off the ground. When the operator releases the valve, it automatically returns to the preset orifice position to provide the desired flotation.

This application is a division of application Ser. No. 07/324,364, filed15 Mar. 1989, Now U.S. Pat. No. 4,920,732.

ASSIGNMENT

The entire right, title and interest in and to this application and allsubject matter disclosed and/or claimed therein, including any and alldivisions, continuations, reissues, etc., thereof are, effective as ofthe date of execution of this application, assigned, transferred, soldand set over by the applicant(s) named herein to Deere & Company, aDelaware corporation having offices at Moline, Ill., 61265, U.S.A.,together with all rights to file, and to claim priorities in connectionwith, corresponding patent applications in any and all foreign countriesin the name of Deere & Company or otherwise.

BACKGROUND OF THE INVENTION

The present invention relates generally to hydraulic lift systems, andmore specifically to a hydraulic lift system including an adjustablevalve operable for both hydraulic lift and hydraulic weight transferfunctions.

Machines such as, for example, a front-mounted mower utilize both a liftsystem to raise and lower an implement relative to a vehicle and amechanical or hydraulic device to transfer weight from the implement tothe vehicle during operation. Some machines utilize chains, cables orsprings, or a combination thereof, to provide weight transfer. With somefront-mounted mower arrangements, an extension spring is attached to theframe of the vehicle and to the implement to transfer implement weightonto the vehicle drive wheels for better traction and to reduce theimplement weight on the ground for better flotation. Other structuresinclude a torsion spring mounted on the pivot axis of push arms whichare connected to the implement to transfer implement weight to thevehicle drive wheels.

Another weight transfer arrangement which is utilized on presentlyavailable John Deere front-mounted mowers includes a weight transfervalve providing an adjustable flow restriction downstream from theoperator control valve connected to the hydraulic lift cylinders. Byrotating the weight transfer valve, the flow restriction is adjusted toprovide a preselected charge pressure to the lift cylinder which, inturn, provides the desired lift for transferring the weight of theimplement to the vehicle drive wheels.

The mechanical weight transfer devices require exterior hardware whichdetracts from the appearance of the vehicle. Mounting brackets are alsoneeded with the mechanical devices, and the implement lift force canvary substantially as the implement goes up and down over the terrain.The adjustment of the lift force with mechanical devices can also bedifficult and non-precise.

Although the hydraulic system for transferring weight is relatively morecompact and easier to adjust than the mechanical systems, two valveshave been necessary to provide both the adjustable weight transferfunction and the lift function. The additional valve significantlyincreases the cost and complexity of the hydraulic system. In addition,presently available weight transfer valves permit the operator toconveniently lift the implement from the ground and maintain theimplement in the lifted position rather than following the recommendedprocedure of maintaining the implement at least partially supported onthe ground for increased machine stability. Although the lift or fullfloat position is required on the weight transfer valve to give theoperator the capability to climb a curb or small hill or to load theimplement onto a trailer, costly ballast is required on the machine tocounterbalance the weight of the implement when it is transported in thefloat position against recommended procedures.

BRIEF DESCRIPTION OF THE INVENTION

It is therefore an object of the present invention to provide animproved lift cylinder structure for providing weight transfer and fulllift functions. It is another object to provide such a structure whichovercomes the aforementioned problems. It is yet another object of theinvention to provide such a structure which is easy to adjust, providesuniform flotation over ground variations, and gives the operator thecapability of climbing a curb, small hill or trailer ramp whileencouraging operation in a partial flotation mode during transport.

It is still another object of the present invention to provide animproved lift cylinder structure with both weight transfer and liftfunction capabilities. It is a further object to provide such astructure which is more compact and substantially less costly than mostpreviously available weight transfer and lift systems. It is a furtherobject to provide such a structure wherein weight transfer is easilyadjustable and wherein the operator has the option of momentarilyproviding full flotation, with automatic return to the preset flotationposition. It is a further object to provide such a structure whereinfull flotation is provided only when the operator positions the valveagainst a bias and holds it in that position, thereby discouraging theoperator from continuous operation of the machine in the full floatposition.

It is still a further object of the present invention to provide animproved control valve for a lift cylinder structure which provides aweight transfer function. It is another object to provide such a valvewith a control which is movable both axially and rotationally to provideadjustable weight transfer and full lift capabilities in a single valvestructure. It is another object to provide such a valve which is biasedtoward a preselected weight transfer position but is movable against thebias to a full lift position. It is another object to provide such avalve which automatically returns to the preselected weight transferposition when the operator releases the valve.

It is still another object of the present invention to provide animproved control valve for a lift cylinder structure which provides aneasily adjustable weight transfer function as well as a momentary fulllift or full float capability. It is a further object to provide such avalve which utilizes both rotational and axial movement from a singlecontrol point to adjust the weight transfer and provide the liftcapability.

In accordance with the above objects, a hydraulic system for a vehiclehaving an implement mounted for vertical movement thereon includes alift cylinder connected between the vehicle and the implement and asingle control valve connected downstream of the lift cylinder foradjustably restricting flow from the cylinder in a closed centerhydraulic system. The valve acts as a bleeder for the lift cylinder andincludes a control knob which is rotatable to adjust the amount ofrestriction which, in turn, determines the amount of weight transferfrom the implement to the vehicle provided by the lift cylinder. Theknob is also movable axially against the bias of a spring to directhydraulic fluid flow to the lift cylinder to lift the implement. Tomaintain the implement in the fully lifted or full float position, theoperator must hold the knob against the bias. Releasing the knob returnsthe valve to the weight transfer position wherein the implement islowered to the ground with the predetermined amount of weight transferprovided. The bias helps assure that the operator will operate themachine with the implement lowered. When it is necessary to move theimplement to the full float condition, the operator may do so by movingthe knob in the axial direction.

The valve includes a valve body having a central bore with an inlet portlocated at the lower end of the bore and an outlet port offset slightlyabove the inlet port. A plunger assembly is slidably received within thevalve bore and is biased by a spring to a normal operating positionwherein an inlet to a poppet opens into the inlet port and an outlet tothe poppet opens into the output port. The poppet provides an adjustablerestriction to fluid flow through the valve. A spring normally biasesthe poppet toward a restricted position, and the tension of the springis adjustable by rotating the valve control knob. By rotating the knobin one direction, the tension on the spring is relieved to let thepoppet move away from the inlet port and thereby create less restrictionto hydraulic fluid flow so that less weight is transferred from theimplement to the vehicle. Rotating the knob in the opposite directionincreases the spring tension and forces the poppet back into the orificeto create full weight transfer. When the plunger assembly is pulledupwardly, the inlet of the poppet no longer aligns with the inlet portto thereby block off all flow of fluid through the valve. With the valveblocked, all of the fluid flow is directed to the lift cylinder to raisethe implement relative to the vehicle. The plunger assembly is biased tothe normal operating position with sufficient force to discourage theoperator from operating the vehicle with the implement in the fullyraised position. When the knob is released, the valve returns to thepreselected adjusted position to provide the desired implementflotation.

The lift cylinder structure is relatively simple and compact inconstruction and eliminates multiple valves. Flotation adjustments maybe made quickly and precisely. The lift force on the implement remainsconstant even over irregular ground surfaces to provide predictableimplement flotation. The lift force can be easily adjusted toaccommodate changes in terrain, conditions and operating speeds.Unsightly exterior hardware is eliminated. The valve encourages theoperator to operate the machine with the implement lowered to the groundin a partial flotation condition. It also gives him the capability ofmomentarily providing full float for climbing a curb, hill or loadingramp.

These and other objects, features and advantages of the presentinvention will become apparent to those skilled in the art from thedescription which follows and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a vehicle with an implement attached theretoand with the lift cylinder structure of the present invention indicatedschematically.

FIG. 2 is a rear view of a control valve constructed in accordance withthe teachings of the present invention.

FIG. 3 is a sectional view of the control valve of FIG. 2.

FIG. 4 is a top view of the valve of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a vehicle 10 having an implement 12connected to the front end thereof by lift system 14. The lift system 14includes lift arms 18 pivotally connected to the forward end of thevehicle frame and extending forwardly therefrom to a connection at 22with the implement 12. A hydraulic lift cylinder 26 has a base endconnected to the frame of the vehicle 10 and a rod end connected to thelift system 14. The device is shown as a front-mounted mower, althoughit is to be understood that the lift structure of the present inventionmay also be utilized with other types of equipment.

The lift cylinder 26 is connected by a line 28 to the output of a sourceof hydraulic fluid under pressure 30 located on the vehicle 10. Anadjustable operator control valve 40 is connected between the line 28and a reservoir 42 by a line 29.

The valve 40 adjustably bleeds fluid flow from the lift cylinder 26 toadjust the cylinder pressure which tends to rotate the lift arms 18upwardly about their pivotal connections with the vehicle 10. The valve40 preferably is supported by the instrument panel housing of thevehicle and includes a single control movable in two differentdirections, as will be described in detail below, to provide both weighttransfer of the implement 12 to the vehicle 10, and a short-term fulllift or full flotation function wherein flow from the cylinder 26 issubstantially blocked so that the cylinder lifts the implement 12 to thefully raised position. Movement of the control in one of the directionsadjusts the amount of restriction to fluid flow from the cylinder 26 toreservoir to thereby adjust the amount of weight transfer providedduring normal operation of the implement 12. Movement of the control ina second direction blocks substantially all flow through the valve thusdirecting hydraulic fluid into the lift cylinder 26 to thereby rotatethe lift arms 18 upwardly and raise the implement 12 from the ground.Preferably, the valve 40 is heavily biased toward the flotationposition, and the full lift function is only provided when the operatorholds the control against the bias.

Referring now to FIGS. 2-4, the construction of the valve 40 will bediscussed in detail. In the embodiment shown, the valve 40 includes avalve body 46 having a central bore 48 with an inlet port 52 openingradially into the lower central portion of the bore 48 and connected tothe line 28. An outlet port 56 connected to the line 29 extends radiallyfrom the central bore 48 on the back side of the valve body 46 (FIG. 2)at a location offset slightly above the port 52.

A valve spool or plunger assembly 60 (FIG. 3) is slidably receivedwithin the central bore 48 and is supported and retained therein bysealed bearing assemblies 62 and 64 located at the upper and lower ends,respectively, of the valve body 46. The ends of the central bore 48 areslightly enlarged to receive shoulders 66 located on the bearingassemblies 62 and 64. Snap rings 68 secure the bearing assemblies inposition. The lower end of the spool 60 includes a reduced diameterportion 70 slidably received in and sealed by the lower bearing assembly64. A threaded shaft 74 projects upwardly from the upper end of thespool 60 through the center of the upper bearing assembly 62 and outbeyond the upper end of the valve body 46. The lower bearing assembly 64prevents movement of the spool 60 downwardly beyond the normal operatingposition shown in FIG. 3. A retaining ring 76 is secured to the shaft 74and contacts the lower end of the upper bearing assembly 62 to limitupward movement of the spool 60.

The upper end of the spool 60 is internally threaded at 80, and anadjusting member 82 is threaded into the spool 60. The lower end of thethreaded shaft 74 is fixed to the member 82. A control knob 88 isthreaded onto the upper end of the shaft 74 and secured thereon by a setscrew 92. By rotating the control knob 88 in the clockwise direction,the adjusting member 82 is threaded downwardly into the upper end of thespool 60. Rotation in the opposite direction moves the member 82upwardly relative to the spool 60. A stop collar 94 is fixed to theupper end of the spool 60. The ring 76 contacts the collar 94 to limitthe distance that the member 82 can be threaded downwardly. The top ofthe member 82 abuts against the bottom of the collar 94 to limit theupward unthreading of the member 82.

The control end of the spool 60 includes a radially extending bore 102which aligns with the inlet port 52 when the valve is in the normaloperating position as shown in FIG. 3 and by the solid lines in FIG. 2.An axial bore 104 opens upwardly from the bore 102 into variable orificestructure indicated generally at 106 which, as shown in FIG. 3, includesa poppet 110 with an inlet opening downwardly into the bore 104 and anoutlet aligned with the outlet port 56. The poppet 110 is biased towarda closed position by a tension spring 114 which is compressed betweenthe poppet 110 and the lower end of the adjusting member 82. Therefore,one can see as the control knob 88 is rotated in the clockwise directionto move the adjusting member 82 downwardly, the force of the spring 114acting downwardly on the poppet 110 increases and to increase therestriction to fluid flow from the inlet port 52 through the valve tothe outlet port 56. Rotating the control knob 88 in the oppositedirection relieves the pressure of the spring 114 and lets the poppet110 move away from the inlet to create less restriction to fluid flowthrough the valve.

To prevent rotation of the spool 60 within the central bore 48 of thevalve, a longitudinal groove 118 is formed in the surface of the spool,and a plug assembly 122 threaded into an aperture opposite the inletport 52 includes a projection 124 which is received within the groove118. The groove 118 and plug assembly 122 permit axial movement of thespool 60 while preventing relative rotation between the spool and thevalve body.

A compression spring 130 encircles the lower end of the threaded shaft74 and is compressed between the lower end of the bearing assembly 62and the upper end of the spool 60 to bias the spool downwardly towardthe position shown in FIG. 3 wherein the inlet port 52 is aligned withthe bore 102. By pulling on the knob 88 in the upward direction (brokenlines, FIG. 2), the spool 60 is pulled upwardly against the bias of thespring 130 until the bore 102 is completely out of alignment with theinlet port 52 and the spool completely blocks the inlet port. Contactbetween the ring 76 and the bearing assembly 62 limits upward axialmovement of the spool 60. When the inlet port 52 is blocked, fluid flowthrough the valve is completely cut off so that all of the flow from thepump 30 is directed through the line 28 into the lift cylinder 26 toraise the implement 12 from the ground. When the control knob 88 isreleased, the spring 130 biases the spool 60 back to the normaloperating position wherein the preselected amount of flotationdetermined by the rotational position of the control knob 88 isprovided, and the implement returns to ground contact with some of theweight of the implement being transferred to the vehicle 10. If moreflotation is desired, the operator simply rotates the knob 88 in theclockwise direction to compress the spring 114 and force the poppet 110downwardly. If less flotation is desired, the operator rotates the knob88 in the counterclockwise direction to relieve spring pressure which inturn lets the poppet 110 move away from the inlet port to create lessrestriction so that more fluid is bled from the cylinder 26. A mark 136(FIG. 4) is provided on the face of the knob 88 so that the operator hasan indication of the orifice adjustment. The stop collar 94 limits theamount of knob rotation to slightly less than 360 degrees.

To adjust the restriction, the operator rotates the knob 102 until thedesired amount of lift for the particular operating conditions of thevehicle is provided. Any time the operator wishes to momentarily liftthe implement 12, for example, when he is climbing a curb or a smallhill or loading the unit onto a trailer, he simply pulls the knob 88 tomove the spool 60 axially and completely block fluid flow away from thecylinder 26. The cylinder then retracts completely to lift the arms 18and the implement 12 to the fully raised position. Preferably, theeffort required to lift the knob 88 is sufficient (approximately five toten pounds or more) so that the operator will tend to operate themachine with the implement lowered to the more stable flotation positionin contact with the ground. The range of orifice adjustment provided byrotating the knob 88 is insufficient to provide full lift to theimplement 12 even at the maximum restricted position (wherein the ring76 abuts against the top of the collar 94) when the valve is in thenormal operating position.

Having described the preferred embodiment, it will be apparent thatmodifications can be made without departing from the scope of theinvention as defined in the accompanying claims.

We claim:
 1. A control valve for actuating a hydraulically operated liftstructure to selectively provide a lift function and a weight transferfunction, the valve comprising:a valve body having an inlet port and anoutlet port; a plunger assembly slidably received within the valve bodyand including a control portion movable between a first position whereinfluid flow between the ports is substantially blocked, and a secondposition wherein flow between the ports is adjustably restricted;adjusting means rotatably received within the valve body including anelement yielding biased toward a preselected restricting position, andmeans responsive to rotation of the adjusting means for varying the biasand changing the amount of restriction to flow between the ports whenthe plunger assembly is in the second position; and operator controlmeans including a single control for moving the plunger assembly betweenthe first and second positions and for selectively rotating theadjusting means.
 2. The invention as set forth in claim 1 wherein theplunger assembly is slidable axially within the valve body, and meansfor biasing the plunger assembly toward the second position.
 3. Acontrol valve for actuating a hydraulically operated lift structure toselectively provide a lift function and a weight transfer function froma single control, the valve comprising:a valve body having an inlet portand an outlet port; a plunger assembly slidably received within thevalve body and including a control portion movable between a firstposition wherein fluid flow between the ports is substantially blocked,and a second position wherein flow between the ports is adjustablyrestricted; means rotatably received within the valve body for adjustingthe amount of restriction to flow between the ports when the plungerassembly is in the second position; operator control means for movingthe plunger assembly axially within the valve body between the first andsecond positions and for selectively rotating the means for adjustingthe amount of restriction, means for biasing the plunger assembly towardthe second position, and wherein the operator control means comprises asingle knob connected to the plunger assembly.
 4. A control valve foractuating a hydraulically operated lift structure to selectively providea lift function and a weight transfer function from a single control,the valve comprising:a valve body having an inlet port and an outletport; a plunger assembly slidably received within the valve body andincluding a control portion movable between a first position whereinfluid flow between the ports is substantially blocked, and a secondposition wherein flow between the ports is adjustably restricted; meansrotatably received within the valve body for adjusting the amount ofrestriction to flow between the ports when the plunger assembly is inthe second position; operator control means for moving the plungerassembly between the first and second positions and for selectivelyrotating the means for adjusting the amount of restriction; and whereinthe means for adjusting the amount of restriction comprises a poppetconnected between the ports and a spring biasing the poppet to arestricted position, and means for varying the spring pressure.
 5. Theinvention as set forth in claim 4 wherein the means for varying thespring pressure comprises a threaded member responsive to rotation ofthe operator control means for movement relative to the poppet, andwherein the spring comprises a coil spring compressed between the poppetand the threaded member.
 6. The invention as set forth in claim 5wherein the plunger assembly includes a control portion having anopening aligning with one of the ports when the assembly is in thesecond position and wherein the poppet and spring are supported withinthe plunger assembly.